An outer surface of a medical elastic tubular body such as catheter is applied with a coating material for smooth insertion into a blood vessel and for protecting the elastic tubular body itself.
Ordinary coating application methods include dip coating, brushing, non-electrostatic spray coating, and electrostatic spray coating. Performances of coating methods can be compared and evaluated with various indexes such as application efficiency (dose to a coating-required part (g)/actual application amount (g)), application speed, coating film uniformity, amount of generated waste, and cost.
Dip coating is a method where a coating object is immersed for a predetermined period in a tank stored with a coating liquid. Dip coating is often used since a coating material can be uniformly applied to the coating object, but its production capacity is limited due to its batch style and an application speed affecting a film thickness. In addition, in dip coating, a coating liquid must be stored in a tank, and, when a period of use of the coating liquid expires, a large amount of the coating liquid must be discarded at a time, thus a cost increases.
Brushing is a method for directly applying a coating liquid to a coating object using a brush or a piece of sponge. Through brushing, a coating liquid can be applied to a desired. part, but it is difficult to create a uniform coating film, and, in addition, its productivity is low.
Non-electrostatic spray coating is a method for spraying, onto a coating object, an atomized coating liquid using a spray gun. Through non-electrostatic spray coating, a coating liquid can be applied to a desired part at a desired film thickness, and its productivity is higher, compared with dip coating and brushing. However, in non-electrostatic spray coating, its application efficiency is in principle relatively low, and only a coating surface facing an application direction can be coated. So, to uniformly apply a coating liquid in a circumferential direction, a plurality of spray guns has to be disposed, or a coating object has to be rotated while applying a coating liquid, thus a complicated device structure is required.
Electrostatic spray coating is a method where, while a voltage is given to a coating liquid for charging, the coating liquid is atomized, and then a coating object is grounded or its electrical potential is made opposite to an electrical potential of the coating liquid to spray the charged coating liquid onto the coating object using an electrostatic spray gun. The charged coating material applies to the coating object by an electrostatic force. Electrostatic spray coating is known its relatively higher application efficiency, thus high productivity,
For example, Patent Document 1 describes a method for performing electrostatic spray coating onto a metallic stent provided on a balloon formed at an end of a catheter. The catheter has a conductor attached to its outer surface so as to make an electric connection between the stent and the conductor. An electric charge is given to the conductor by grounding the conductor or by connecting the conductor to an electric charge opposite to an electric charge of coating particles, and the charged coating particles are electrically attracted and applied to the stent.
Patent Document 2 describes a method for performing coating, using electrostatic spray coating, onto an outer surface of a lumen of a stent press-fitted onto a balloon catheter. With this method, an electric conductive wire is passed into a lumen of a stent-balloon assembly, and an electric charge is given to the electric conductive wire. In addition, the stent is grounded, or given an electrical potential with an electric charge opposite to an electric charge of the electric conductive wire Patent Documents 1 and 2 both describe methods applicable when a coating object has a conductivity. When a coating object is an insulator, to allow an electric charge to easily move, an electro-conductive treatment liquid is normally coated to the coating object beforehand, and then a coating material is applied. However, since such a pretreatment requires time and cost, a method shown below has been developed.
Patent Document 3 describes a method, with an electrostatic spray coating device including a coater for spraying a coating material to a surface of a coating object having a higher electric resistance value, and a high-voltage generator for giving, to the coater, a high voltage having an electrical potential on a polarity, for supporting the coating object with a support made of an insulator having a higher electric resistance value, and, on a back of a side facing the coater, with the coating object interposed, disposing, in proximity to the coating object, a ground electrode having a ground electrical potential.
Patent Document 4 describes a method, using a coating material having a conductivity or a coating material in which an electrostatic aid is added to lower a resistance value, for mounting a coating object on a stand, a jig, or a conveyor having a conductivity to perform coating from a contact position between the coaling object and the stand, the jig, or the conveyor having a conductivity.